MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
https://doi.org/10.47193/mafis.3422021010609
ABSTRACT. Onboard discards of a fraction of the catch can be considered one of the main
issues related to bottom trawling fisheries. The magnitude and composition of the discards still need
to be better understood. We assessed the industrial bottom pair trawling fishery’s discards from
southern Brazil by monitoring 159 fishing hauls during four fishing trips. From the 318.9 mt cap-
tured, 77.7 t were discarded (24%). The discards per haul were highly variable, on average 488.9 kg
(95% CI: 433.6-544.2 kg) and 31% (95% CI 28-34%) of the total. The rejected catch comprised 64
species, 37 teleosts (78.4% in weight) and 13 elasmobranchs (21.3% in weight), besides crus-
taceans, mollusks, cnidarians, and echinoderms. The three most commercially important species in
the region (Umbrina canosai, Cynoscion guatucupa, and Micropogonias furnieri) accounted for
13% of the discarded biomass, and most of them were individuals under 20-25 cm. The discard rates
and species composition did not change over the last 40 years; however, the discarded biomass for
both teleost fishes and elasmobranchs decreased sharply, reflecting the abundance decrease of these
groups in the region. This work highlights the need for management measures to reduce the bottom
pair trawling fishery discards in southern Brazil.
Key words: Bycatch, discard rates, endangered species, juvenile fish.
Evaluación de las capturas descartadas de la pesquería de arrastre de fondo a la pareja de
fondo en el sur de Brasil
RESUMEN. Los descartes a bordo de una fracción de la captura pueden considerarse uno de los
principales problemas relacionados con las pesquerías de arrastre de fondo. Aún es necesario com-
prender mejor la magnitud y composición de los descartes. Evaluamos los descartes de la pesca
industrial de arrastre de fondo a la pareja en el sur de Brasil mediante el seguimiento de 159 lances
de pesca durante cuatro salidas de pesca. De las 318,9 tm capturadas, se descartaron 77,7 t (24%).
Los descartes por lance fueron muy variables, en promedio 488,9 kg (95% CI: 433,6-544,2 kg) y
31% (95% CI 28-34%) del total. La captura descartada estuvo compuesta por 64 especies, 37 tele-
ósteos (78,4% en peso) y 13 elasmobranquios (21,3% en peso), además de crustáceos, moluscos,
cnidarios y equinodermos. Las tres especies de mayor importancia comercial de la región (Umbrina
canosai, Cynoscion guatucupa y Micropogonias furnieri) representaron el 13% de la biomasa des-
cartada y la mayoría fueron individuos menores de 20-25 cm. Las tasas de descarte y la composición
de especies no cambiaron durante los últimos 40 años; sin embargo, la biomasa descartada tanto de
peces teleósteos como de elasmobranquios disminuyó drásticamente, lo que refleja la disminución
de la abundancia de estos grupos en la región. En este trabajo se destaca la necesidad de medidas de
gestión para reducir los descartes de la pesca de arrastre de fondo a la pareja en el sur de Brasil.
Palabras clave: Captura incidental, tasas de descarte, especies amenazadas, peces juveniles.
197
*Correspondence:
cardosolg15@gmail.com
Received: 19 April 2021
Accepted: 11 June 2021
ISSN 2683-7595 (print)
ISSN 2683-7951 (online)
https://ojs.inidep.edu.ar
Journal of the Instituto Nacional de
Investigación y Desarrollo Pesquero
(INIDEP)
This work is licensed under a Creative
Commons Attribution-
NonCommercial-ShareAlike 4.0
International License
Marine and
Fishery Sciences
MAFIS
MARINE IMPACTS IN THE ANTHROPOCENE
An assessment of discarded catches from the bottom pair trawling fishery
in southern Brazil
LUIS G. CARDOSO
1, *
, DANIELLE DA SILVEIRA MONTEIRO
1, 2
and MANUEL HAIMOVICI
1
1
Universidade Federal do Rio Grande, Instituto de Oceanografia, Caixa Postal 474, Avenida Itália km 8, CEP 96201-900, Rio Grande,
RS, Brazil.
2
Núcleo de Educação e Monitoramento Ambiental, Rua Maria Araújo, 450, CEP 96207-480, Rio Grande, RS, Brazil.
ORCID Luis G. Cardoso https://orcid.org/0000-0003-1026-0853
INTRODUCTION
Incidental catches and subsequent discards of
marine life are frequent features of many fisheries
worldwide and one of the most important biologi-
cal and political issues faced by modern fisheries
(Gillis et al. 1995; Bellido et al. 2011). Regulation
on discards is not common in most fishing juris-
dictions (Hall and Mainprize 2005; FAO 2011).
However, discards are considered a waste of liv-
ing resources, and their ecological consequences
are still not fully understood (Heath et al. 2014).
Despite trawling fisheries present different
métiers, its characteristics of low selectivity gen-
erally generate unwanted catches of species
besides the targeted ones (Davie and Lordan 2011;
Samy-Kamal et al. 2014). The decision to discard
is a function of the relative costs and benefits of
storing and landing fish or rejecting it (Pascoe
2000). For species without commercial interest,
this decision is quite simple since, from the fish-
ers’ point of view, there are no benefits associated
with landing the discard. For species with a com-
mercial interest, the decision to discard depends
on several factors: the price that the catch can
attain, the cost of landing it, and the opportunity
cost of stocking fish on board (Clucas 1997).
Between 2010 and 2014, on average, 9.1 mil-
lion t were discarded globally per year, with a
massive heterogeneity between fishing gears and
regions (Pérez Roda et al. 2019). The trawling
fleets accounted for 4.2 million t per year. The
shrimp trawling fisheries present the highest dis-
card rate by weight (~ 50% of global catch), and
they are exceptionally high in tropical and sub-
tropical regions. Still, otter board and bottom pair
trawling’s rate of discards were also considerable
(Pérez Roda et al. 2019).
Regarding the marine and estuarine fisheries in
southern Brazil, several authors quantified the dis-
cards rates (Haimovici and Maceira 1981;
Haimovici and Habiaga 1982; Haimovici and
Mendonça 1996; Vieira et al. 1996; Dumont and
D’Incao 2011; Rezende et al. 2019). Haimovici
and Habiaga (1982) quantified in detail the bottom
pair trawling fisheries discards from two commer-
cial fishing trips occurring in the summer (sum) of
1978 (Haimovici and Maceira 1981) and the
spring (spr) of 1979. In the summer cruise, the dis-
card rate was more significant, 40% of the catch’s
weight, and 26% in the spring. In terms of species
composition by weight of the rejected catch, the
dominance was of several species of small sharks
and rays (sum: 30% and spr: 56%); of largehead
hairtail Trichiurus lepturus (sum: 19% and spr:
12%) and the Argentine croaker Umbrina canosai
(sum: 7% and spr: 8%). Discards in numbers of
juveniles of the three most important fish species
varied between seasons, reaching high percent-
ages: sum: 70% and spr: 26% of U. canosai, sum:
63% and spr: 37% of striped weakfish Cynoscion
guatucupa, sum: 66% and spr: 37% of king weak-
fish Macrodon atricauda. Studies that aged U.
canosai, C. guatucupa, and M. atricauda have
shown that discarded individuals were juveniles
from 1 to 1.5 years old who still were not fully
recruited to the adult stock. Other species such as
banded croaker Paralonchurus brasiliensis and
the bluewing searobin Prionotus punctatus also
occurred in the discarded catch.
The ‘Pescadores por Natureza’ project carried
out by the non-governmental organization Núcleo
de Educação e Monitoramento Ambiental
(NEMA) sampled several commercial fishing
trips of bottom pair trawling by onboard scientific
observers. This study aimed to assess the discard-
ed catches in a qualitative and quantitative way
and compare the results with those observed by
Haimovici and Habiaga (1982) three decades ago.
MATERIALS AND METHODS
We analyzed data from 159 hauls collected by
onboard scientific observers during four bottom
198
MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
pair trawling fishing trips carried out from Santa
Marta Grande cape (28° 37′ S) to Chuí (33° 41′ S)
between 10 and 48 m deep (Figure 1). The trips
occurred between November 2011 and May 2012.
Three trips lasted 6, 14, and 13 days, respectively,
and took place in two industrial fishing boats
measuring 23 m in length, with 360 HP engines
and a storage capacity of 57 t of fish each. The
fourth trip lasted 19 days and took place in a pair
of vessels of 25 m in length, with 360 HP engines
and a storage capacity of 70 t each.
Bottom trawling nets were made of nylon mul-
tifilament and had headropes measuring 38 m and
footropes 45 m. The net measured 56 m in length,
the bellies 28 m, and the cod-end 28 m. The mesh
of the cod-end and the overcoat were 9 cm and
20 cm between opposite knots, respectively.
Hauls lasted between 2.25 and 7 h long (on
average 4 h 18 min) and the trawling speed was
of approximately 4 nautical miles per hour. After
each haul, four fishermen selected the catch to be
stored and packed it in hampers. The discarded
part of the catch was thrown back to the sea
through the deck hatches. To make the fisher-
men’s work compatible with the samplings, the
observer recorded the number of hampers per
species of the stored catch and visually estimated,
together with the vessel’s master, the amount of
discarded catch. Whenever possible, from each
sampled haul, the observer collected a 20 kg box
from the catch to be discarded for species dis-
crimination, counting, weighing, and measuring
the individuals. Species identifications were
made based on the observers’ previous experi-
199
CARDOSO ET AL.: DISCARDED CATCHES FROM BOTTOM PAIR TRAWLING IN SOUTHERN BRAZIL
Figure 1. Area with monitored bottom pair trawling fishing hauls in southern Brazil. Crosses represent hauls in which the per-
centage of total discards was estimated. Solid circles represent hauls in which the composition of discards was sampled.
Santa Catarina
Rio Grande do Sul
Brazil
Uruguay
Southwestern
Atlantic
Ocean
28°
30°
32°
34°
S
48°50°52°54°56°58°W
N
50 50 100 1500km
ence in sampling landings and with the help of
identification guides for species present in the
coastal waters of southern Brazil by Figueiredo
and Menezes (1978, 1980); Menezes and
Figueiredo (1980, 1985) and Fischer et al. (2011).
Unidentified species were labeled and pho-
tographed for later identification.
For each 10 m depth bins, the number of
species in the discarded catch was calculated (R =
species richness) and the Shanon-Weaver (H)
Shanon and Weaver (1949) diversity index,
defined as:
H = (n log(n) f
i
log( f
i
)) / nt
where k is the number of species present in the
discards, n is the total number of individuals of all
species, and f
i
is the number of individuals of
each species.
The discarded catch was calculated as average
total catches per species, stored catches per
species, discarded catches per species, and dis-
carded rates per species. These metrics were com-
pared with those calculated by Haimovici and
Habiaga (1982) for two fishing trips with the
same fleet realized in the 1970s.
i 1=
å
k
RESULTS
Discards quantification
From a total of 318.9 t caught in the 159 mon-
itored hauls, 77.7 t were discarded, 24% of the
total. On average, 488.9 kg (± 55.3 kg) were
dumped per haul, however, hauls with between
200 and 400 kg of discards were more frequent
(23%) (Figure 2 A). On average, 31% of the total
catch was discarded (± 3%, 95% confidence
interval). In 26.2% of the hauls, the discarded
catch was less than 20% of the total, in 25% was
between 20 and 29.9%, and in 48.8% was 30% or
more (Figure 2 B).
The discards varied according to haul’s depths
(Figure 3). The discarded catch percentage was
higher between 10 and 20 m (40%) and showed
a decreasing trend with increasing depths (Fig-
ure 3 A). Total discards (kg) were not signifi-
cantly different between 10 and 40 m deep (Fig-
ure 3 B).
Each monitored fishing trip took place in a dif-
ferent season in the southern hemisphere, spring
2011, summer and autumn 2012. Average discard
rates for each season were 31.6% in spring / 2011
200
MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
Figure 2. Number of hauls per bin of 200 kg (A) and per bin of 10% (B) of discarded catch on the bottom pair trawling fishing
trips monitored in southern Brazil.
0
10
20
30
40
50
Percentage of discards intervals (%)
0
10
20
30
40
50
Number of hauls
Discarded catch intervals (weight kg)-
0-200
200-400
400-600
600-800
800-1,000
> 1,000
0-10
10-20
20-30
30-40
50-60
60-70
40-50
70-80
80-90
A
B
(n = 22, sd = 0.19), 35.7% in summer / 2012 (n =
109, sd = 0.15) and 15.2% in autumn / 2012 (n =
26, sd = 0.11). Values differed significantly
between seasons (ANOVA, p < 0.05). A Tukey
test showed that the difference was between
autumn and spring and summer. Spring and sum-
mer did not differ.
Composition of the discarded catch
In 47 of the monitored hauls, samples were
taken from the discarded catch. In each sample,
species were identified to the lower taxon, and
individuals of each species were counted,
weighed (g), and measured (total length TL in
mm). Observers identified 64 species, 37 of
which were teleost, 13 elasmobranch, 11 crus-
taceans, three mollusks in addition to cnidarians
and echinoderms that were not identified at the
species level (Table 1).
Teleost fish represented 92.5% in number and
78.4% in weight. Elasmobranchs accounted for
5% in number and 21.3% in weight, and crus-
taceans (crabs and shrimps) accounted for 1.6%
in number and 0.8% in weight. Molluscs, cnidar-
ians, and echinoderms represented less than 1%
of the total.
Among the teleost fishes, the most abundant in
weight was the banded croaker P. brasiliensis
(18% in number and 20% in weight of teleost fish
and present in 62% of the hauls). The most com-
mon species was the largehead hairtail T. lep-
turus, present in 79% of the hauls, representing
9% in number and 20% in weight. Seven species
represented 80% in number, and 70% of the total
rejected teleosts’ weight (Figure 4 A).
201
CARDOSO ET AL.: DISCARDED CATCHES FROM BOTTOM PAIR TRAWLING IN SOUTHERN BRAZIL
Figure 3. Average discards per depth bin in the bottom pair trawling monitored hauls in southern Brazil. A) Average percentage
of discards per haul. B) Average discards in weight per haul. Vertical bars indicate confidence intervals of the means at
the 95% level.
0
10
20
30
40
50
0
200
400
600
800
1 000,
Depth intervals (m)
A
B
10-20 20-30 30-40 40-50
10-20 20-30 30-40 40-50
Percentage of discards
(%)intervals
Discarded catch intervals
(weight kg)-
202
MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
Table 1. Number of individuals, total weight, average weight, and frequency of occurrence (FO) of each of the species sampled
from the discarded catches in 47 hauls of bottom pair trawling fishing trips monitored in southern Brazil.
Taxonomic Species Number of individuals Total weight Average weight FO (%)
group on the samples (kg) (kg)
Elasmobranch Sympterygia acuta 174 71.31 0.41 40
Elasmobranch Atlantoraja platana 51 28.2 0.55 13
Elasmobranch Atlantoraja cyclophora 28 16.6 0.59 4
Elasmobranch Zapterix brevirostris 25 5.36 0.21 28
Elasmobranch Psammobatis sp. 23 9.94 0.43 11
Elasmobranch Sphyrna lewini 8 0.3 0.04 2
Elasmobranch Sympterygia bonapartii 7 2.5 0.36 6
Elasmobranch Squatina gugenheim 7 5.5 0.79 9
Elasmobranch Atlantoraja castelnaui 4 1.94 0.49 9
Elasmobranch Mustelus sp. 4 0.42 0.11 9
Elasmobranch Pseudobatos horkellii 4 0.89 0.22 9
Elasmobranch Myliobatis sp. 3 0.2 0.07 2
Elasmobranch Gimnura altavela 7 2.23 0.32 2
Teleost Paralonchurus brasiliensis 1,148 112.43 0.10 62
Teleost Stephanolepis hispidus 1,097 46.57 0.04 53
Teleost Cynoscion guatucupa 922 46.05 0.05 40
Teleost Trichiurus lepturus 562 109.6 0.20 79
Teleost Umbrina canosai 523 36.76 0.07 38
Teleost Prionotus punctatus 448 33.21 0.07 51
Teleost Trachurus lathami 448 9.25 0.02 11
Teleost Steliffer sp. 176 15.5 0.09 15
Teleost Peprilus paru 153 14.94 0.10 45
Teleost Micropogonias furnieri 149 14.62 0.10 21
Teleost Dules auriga 120 10.18 0.08 32
Teleost Macrodon atricauda 114 12.16 0.11 26
Teleost Brevoortia pectinata 107 47.36 0.44 23
Teleost Ctenosciaena gracilicirrhus 89 10 0.11 2
Teleost Porychthys porosissimus 63 5.06 0.08 11
Teleost Chylomicterus spinosus 46 7.67 0.17 17
Teleost Cynoscion jamaicensis 45 4.05 0.09 6
Teleost Urophycis brasiliensis 44 6.24 0.14 34
Teleost Mullus argentinus 40 1.751 0.04 23
Teleost Percophis brasiliensis 28 2.17 0.08 19
Teleost Syngnathus folletti 28 1.55 0.06 9
Teleost Paralichtys orbignianus 24 4.7 0.20 11
Teleost Oncopterus darwinii 13 0.85 0.07 9
Teleost Paralichthys patagonicus 10 0.66 0.07 9
Among the elasmobranchs, the most abundant
and frequent species was the stingray Symptery-
gia acuta (50% in number, 49% in weight of elas-
mobranchs, and present in 40% of the hauls).
Five species accounted for 87% of the abundance
in number and 90% by weight of the total of dis-
carded elasmobranchs: stingray S. acuta, the
Atlantic stingrays Atlantoraja platina, and A.
cyclophora, Zapterix brevirostris, and Psammo-
batis spp. (Figure 4 B).
Among the crustaceans, the most abundant
species was the swimmer crab Ovalipes trimacu-
latus which represented 32% in number and 62%
by weight of the total crustaceans and was present
in 11% of the hauls. The most frequent species
was the hermit crab Loxopagurus loxochelis,
which was present in 17% of the hauls and repre-
sented 20% of the total number of individuals in
the crustacean group (Figure 4 C).
203
CARDOSO ET AL.: DISCARDED CATCHES FROM BOTTOM PAIR TRAWLING IN SOUTHERN BRAZIL
Table 1. Continued.
Taxonomic Species Number of individuals Total weight Average weight FO (%)
group on the samples (kg) (kg)
Teleost Astroscopus sexspinosus 8 0.85 0.11 9
Teleost Pagrus pagrus 7 0.2 0.03 6
Teleost Gymnachirus nudus 5 0.2 0.04 4
Teleost Selene sp. 4 0.00 9
Teleost Citharichtays spilopterus 3 0.2 0.07 2
Teleost Engraulius anchoita 3 0.00 4
Teleost Lagocephalus laevigatus 3 0.45 0.15 2
Teleost Menticirrhus americanus 3 0.36 0.12 6
Teleost Zalieutes mcgintyi 3 0.033 0.01 6
Teleost Balistes capriscus 1 0.00 2
Teleost Paralichtys isosceles 1 0.13 0.13 2
Teleost Oligoplites saliens 1 0.5 0.50 2
Crustacea Arenaeus cribrarius 2 0.093 0.05 4
Crustacea Dardanus insignis 6 0.00 4
Crustacea Hepatus pudibundus 3 0.00 2
Crustacea Ovalipes trimaculatus 38 4.25 0.11 11
Crustacea Portunus spinimanus 10 1 0.10 9
Crustacea Artemesia longinaris 2 0.00 2
Crustacea Callinectes sapidus 18 0.159 0.01 15
Crustacea Libina spinosa 5 0.24 0.05 2
Crustacea Loxopagurus loxochelis 24 0.31 0.01 17
Crustacea Scyllarides sp. 4 0.31 0.08 6
Mollusc Adelomelon brasiliensis 3 0.2 0.07 2
Mollusc Doryteuthis sp. (lulas) 34 0.7 0.02 17
Mollusc Octopus tehuelchus 2 0.1 0.05 2
Cnidaria 7 14.4 2.06 4
Echinoderm 6 0.4 0.07 2
204
MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
Figure 4. Specific composition of the discarded catch from bottom pair trawling fishing trips monitored in southern Brazil.
Percentage in number and weight of species to the total in the taxonomic group. Teleost (A); elasmobranchs (B); crus-
taceans (C).
Frequency in number Frequency in weight
A
B
C
Other sp.
Dardanus insignis
Ovalipes trimaculatus
Portunus spinimanus
Callinectes sapidus
Loxopagurus loxochelis
Crustaceans
Elasmobranchs
Other sp.
Sympterygia acuta
Atlantoraja platana
Atlantoraja cyclophora
Zapterix brevirostris
Psammobatis sp.
Teleosts
O.ther sp
Stephanolepis hispidus
Cynoscion guatucupa
Trichiurus lepturus
Umbrina canosai
Prionotus punctatus
Trachurus lat amih
Paralonchurus brasiliensis
Species richness and diversity of the discarded
catch per depth range
Both the number of species and the diversity
were higher between 20 and 30 m deep (R = 47;
H = 1.04) (Figure 5). No pattern was observed
between the number of species and the diversity
index, as between 30 to 40 m despite a smaller
number of species (< 30), the diversity index was
higher because the number per species did not
differ much. The lack of pattern is because the
diversity index considers, in addition to the num-
ber of species, the number of individuals per
species, and the more equal this number is, the
greater the diversity index. The lower diversity
was observed between 10 to 20 m, in which a few
species dominate. In this depth range, despite the
discards being composed of more than 40 species,
the diversity index is low since only two species,
P. brasiliensis and T. lepturus, represent 63.2% of
the total number of individuals.
Discards of the species of commercial interest
Top five commercial interest species accounted
for 27% in number and 21% by weight of the dis-
carded catches of teleost fishes. Among the dis-
carded teleost fishes, M. furnieri represented 2%
in number and 3% in weight, U. canosai 8% and
7%, C. guatucupa 14% and 8%, M. atricauda 2%
and 2% and Urophycis brasiliensis 1% and 1%,
respectively.
For the first three species (M. furnieri, U.
canosai, and C. guatucupa), discarded individu-
als were composed mainly of fishes smaller than
200 mm TL (Figure 6), corresponding to sexually
immature individuals with a maximum of two
years old (Haimovici and Reis 1984; Miranda and
Haimovici 2007; Cavole and Haimovici 2015).
For M. atricauda, discarded individuals were also
mainly composed of fishes smaller than 200 mm
TL (Figure 6), which correspond to a maximum
of one year old and can be sexually mature if
males and sexually immature if females (Cardoso
and Haimovici 2014). For U. brasiliensis, the dis-
carded individuals were composed mainly of
fishes smaller than 300 mm TL, which, if females
can reach two years old and males more than
three years old, included sexually mature organ-
isms (Cavole et al. 2018).
205
CARDOSO ET AL.: DISCARDED CATCHES FROM BOTTOM PAIR TRAWLING IN SOUTHERN BRAZIL
Figure 5. Shannon diversity indices (H) and number of species present in samples from the discarded catch per depth range.
10
20
30
40
50
0.8
0.9
1.0
1.1
10 -20 20 -30 30 -40 40 -50
Number of species
Depth intervals (m)
H
Number of species
H diversity index
Comparison with the 1970s
Total discard rates presented in this work did
not differ significantly from those estimated by
Haimovici and Maceira (1981) and Haimovici
and Habiaga (1982) three decades ago from com-
mercial bottom pair trawling fishing trips samples
(Table 2). However, they differed for some
species, e.g. U. canosai was much more frequent
in the discarded catches in the 1970s while P.
brasiliensis has been more frequent in recent
years (Table 2).
In absolute terms, both the stored total catches
and the discarded catch per hour of trawling have
decreased along time (Table 2). The most evident
change can be seen in the discarded catch per
unit of effort for the juveniles of U. canosai, C.
guatucupa, and M. atricauda and in total catches
of elasmobranch species, which have decreased
significantly.
DISCUSSION
The analysis of the discarded catch is essential
to evaluate the real impact of fishing on the fish
stocks and also to assess the impact of fishing on
the entire marine biological community, which is
vulnerable to the fishing gears (Heath et al. 2014;
Hiddink et al. 2017).
The industrial bottom pair trawling and the
double rig bottom trawling affect both juveniles
of commercially important species and the dem-
ersal biodiversity of the continental shelf of
southern Brazil (Haimovici and Habiaga 1982;
Haimovici and Mendonça 1996). The discard in
kg per haul did not differ between depth ranges,
but the rate between the discard and the total
catch was higher between 10 to 20 m. Between 20
and 30 m deep, discards were composed of a
more significant number of species and a greater
biological diversity. Higher discard rates and bio-
logical diversity highlight the impact of trawling
206
MARINE AND FISHERY SCIENCES 34 (2): 197-210 (2021)
Figure 6. Length composition of stored and discarded indi-
viduals for the five main fishing targets of the bot-
tom pair trawling in southern Brazil.
207
CARDOSO ET AL.: DISCARDED CATCHES FROM BOTTOM PAIR TRAWLING IN SOUTHERN BRAZIL
Table 2. Average total catches (Tot), stored (Sto), discarded (Disc), and discarded rates (%Disc) per species or species groups in bottom pair trawling fishing
trips carried out in southern Brazil during the spring and summer from the 1970s and the 2010s.
Espada-Delfim March 1978 Espada-Delfim Nov.-Dec. 1979 Primavera VII/VIII Jan.-Feb. 2012 Primavera VII/VIII Nov. 2011
Species Tot Stor Disc %Disc Tot Stor Disc %Disc Tot Stor Disc %Disc Tot Stor Disc %Disc
(kg h
-1
) (kg h
-1
) (kg h
-1
) (%) (kg h
-1
) (kg h
-1
) (kg h
-1
) (%) (kg h
-1
) (kg h
-1
) (kg h
-1
) (%) (kg h
-1
) (kg h
-1
) (kg h
-1
) (%)
Micropogonias 105.8 105.8 0 136.6 136.6 0 79.3 70.50 8.87 5 87.5 87.5 0
furnieri
Umbrina 118.5 56.4 62.1 29 342.8 322.9 19.9 8 56.3 44.40 11.83 6 117.2 113.2 4.1 3
canosai
Cynoscion 103.2 87.4 15.8 7 174.7 169.5 5.2 2 79.3 68.90 10.45 6 30.4 26.3 4.1 3
guatucupa
Macrodon 44.6 37.2 7.4 3 30.9 27.6 3.3 1 94.2 82.70 11.48 6 8.3 7.8 0.4 0
atricauda
Trichiurus 42.0 42.0 19 30.9 30.9 12 26.5 1.82 24.66 13 14.1 14.1 11
lepturus
Paralonchurus 19.4 19.4 9 5.3 5.3 2 26.3 26.35 14 3.4 3.4 3
brasiliensis
Prionotus 7.6 2.9 4.7 2 9.5 2.18 7.28 4 14.0 9.0 7
punctatus
Stephanolepis 5.6 5.56 3 27.3 27.3 21
hispidus
Other teleosts 26.8 16.6 6.4 3 33.4 20.4 13.0 5 90.9 62.58 28.33 15 84.4 41.3 43.1 33
Angel sharks 23.3 23.3 0 60.7 28.7 32.0 9.2 9.2 5 2.1 2.1 2
and guitarfish
Rays and 64.3 64.3 30 178.4 178.4 40.4 40.4 22 22.1 0.3 21.8 17
small sharks
Total 547.9 326.7 217.4 40 995.6 734.9 260.7 26 517.5 333.10 184.4 35 410.9 281.4 129.5 35
in the coastal zone on juveniles of commercially
important species, reducing the potential fisheries
in the region and preventing the recovery of
endangered species of elasmobranchs.
This work shows that 33 years after the first
study (Haimovici and Maceira 1981), discard
rates of the bottom pair trawling remain high (>
30%) in the spring and summer in southern
Brazil. Furthermore, the sizes from which the
main species of commercially important teleost
species start to be stored remain the same; in gen-
eral, fish smaller than 20-25 cm are discarded.
The fact that the sizes in which fishes are discard-
ed have not changed allows us to suppose that the
decrease in discard rates of juveniles of the four
main species (Table 2) results from the decrease
in the abundance of the adult stocks, which have
been suffering intense fishing exploitation for
more than seven decades (Haimovici 1998; Vas-
concellos et al. 2006; Haimovici and Cardoso
2016). Regarding the elasmobranchs, total catch-
es decreased moderately but discards remain
high. The reason is not the lack of a market for
small sharks, angelfish, and guitarfish, but the
prohibition of landings that discourage directed
fishing. The decrease of the elasmobranch catch-
es reflects the substantial decline in their abun-
dance recorded in the last decades in the region
(Vooren and Klippel 2005). Some differences
regarding the composition of the discarded catch-
es were verified. Currently, Stephanolepis
hispidus appears the second most abundant
species in the discarded catches from spring and
summer, while it was not significant in the 1970s.
Our results highlight the necessity for manage-
ment measures to mitigate discard in the bottom
pair trawling fisheries in southern Brazil. Dis-
carded catches include small fish that could be
caught in bigger sizes and provide higher yields.
Their catch and disposal in smaller sizes mean
economically inefficient exploitation of critical
natural resources for thousands of fishers, a large
number of industries, and consumers. Further-
more, discards include a large number of endan-
gered species whose ecological importance can-
not be overlooked.
ACKNOWLEDGMENTS
The authors thank the Ministry of Fisheries of
Brazil for the financial support, the fishing com-
panies, captains and crews for making scientific
observers possible on board, and the scientific
observers for their dedication to data collection.
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